Perpendicular magnetic recording (PMR) has become the mainstream technology for disk drive applications beyond 200 Gbit/in2, replacing longitudinal magnetic recording (LMR) devices. The demand for improved performance drives the need for a higher areal density which in turn calls for a continuous reduction in transducer size. A PMR head which combines the features of a single pole writer and a double layered media (magnetic disk) has a great advantage over LMR in providing higher write field, better read back signal, and potentially much higher areal density. Typically, a dual purpose transducer is preferred in which the write head (PMR function) is combined with a read head function in the same structure to form a merged read/write head. The read head may be comprised of a sensor that is a TMR element in which a tunnel barrier layer separates two ferromagnetic (FM) layers where a first FM layer has a fixed magnetization direction and the second FM layer has a magnetic moment that is free to rotate from a direction parallel to that of the “fixed” layer to a direction anti-parallel to the fixed layer and thereby establish two different magnetic states generally referred to as a “0” state and a “1” state. The read process determines which of the two states the TMR element has been written to.
It is well known that the magnetic storage density increases as the gap (flying or fly height) between the magnetic media and a magnetic head such as a merged read/write head decreases. In other words, the so-called air bearing surface (ABS) or exposed plane of the merged read/write head that includes the write pole tip is brought closer to the magnetic media to enhance performance. However, due to non-uniformity in production, the fly height may vary from one slider to the next. Therefore, a low fly height may easily cause one or both of the read head and write head to contact the magnetic media which leads to poor reliability and a damaged device. On the other hand, if the flying height is too high, then poor magnetic performance may result that leads to increased bit error rate, slower read and write operations, and thus a decrease in storage density. Fly height is also influenced by the heat generated when a current is applied to the coils in a write head which tends to cause a thermal expansion of the read/write head toward the magnetic media.
For more controlled heating, at least one heater element is included in a merged read/write head to make adjustments in fly height in response to changes in environmental conditions such as temperature and pressure. A popular design used to control fly height is to position a dynamic fly heater (DFH) opposite the read head or opposite the main pole layer in the write head with respect to the ABS. When the heater is activated, thermal expansion of nearby layers including the write pole in the write head effectively pushes the write pole tip closer to the magnetic media: Likewise, heating of layers in the vicinity of the sensor in the read head causes thermal expansion which results in a read head protrusion toward the magnetic media and thereby reduces the fly height. As disclosed in related application Ser. No. 12/080276, a first dynamic fly heater (DFH) may be included proximate to the sensor in a read head and a second DFH may be positioned proximate to the write pole in a write head for improved fly height control to shorten actuation time and lower power consumption.
Gamma ratio is a critical parameter used to characterize a read/write head because it describes the relationship of mechanical minfly point to magnetic spacing. A lower gamma ratio means a larger gap between the mechanical minfly point and the reader location. An important head design objective is to achieve a gamma as close as possible to 1 which is ideal for tribology and magnetic performance since it keeps the gap between reader and minfly point at a constant value independent of DFH power (actuation). From a drive reliability point, the reader should not be at the minfly point which is the mechanically closet part of the head to the disk because the read head sensor is too sensitive towards mechanical impact. Ideally, the read head should be recessed from the minfly point by at least 0.5 nm.
Under certain conditions, a thin DFH made of a layer having a thickness of about 1000 Angstroms or less, provides a reasonable and predictable dR/R (change in resistance/initial resistance value) when stressed with an elevated current density and increased ambient temperature. However, when DFH thickness is increased to greater than 1000 Angstroms in order to adjust resistance upward, a faster dR increase is observed even at milder stressing conditions. This result indicates a greatly reduced dynamic fly heater lifetime that may be attributed to excessive electro-migration. Thus, a DFH composition is needed that has improved electro-migration behavior which leads to better reliability for thicker heating element films. In addition to reduced electro-migration, a smaller deviation of sheet resistance is needed to provide a tighter power usage distribution. Therefore, an improved DFH composition is required to address both reliability and performance demands in state of the art magnetic heads.
In U.S. Pat. No. 7,239,481, a heating device is disclosed that has a lower Ta adhesion layer formed on an insulation layer in a magnetic head and a heating element layer comprised of NiCr, CrV, or NiFe on the adhesion layer.
U.S. Patent Application 2006/0034013 describes a barrier of W or Ti on a heater wire and a temperature gradient relaxing material formed between turns in the heater element but does not specify the composition of the heater element itself.
U.S. Patent Application 2002/0024774 describes a heater made of an electrical resistance material but does not reveal the composition of the heater material.
In U.S. Patent Application 2007/0230021, NiFe, CuNi, CuSn, or CuMn are employed in a heater film to control flying height in a magnetic head.
U.S. Pat. No. 7,349,170 describes a heater used to control flying height in a magnetic head structure but does not specify a heater composition.